1. Field of the Invention
This invention relates to filters for fluids such as hydraulic oil, transformer oil and lubricating oil, and more particularly to a sealing membrane for use therewith.
2. Prior Art
Oil filters for removing dirt, common residue, and other materials from oil are well known in the art. Such filters are usually packaged either as disposable canisters or as replaceable cartridges. They are generally provided with one or more filter elements which may be of a wound tissue type.
Inflow and outflow connections are provided such that oil entering the canister will flow axially through a filter element, through the interstices between the layers of filter tissue. The dirt and sludge will thus be removed from the oil by the filter tissue. Where there is a single filter element, the oil will flow from one end of the canister to the other, through one end of the filter element, then out the other end of the filter element. The oil is then directed to a central tube which is connected to the outflow connection.
Where dual filter elements are used, the oil will flow from both ends of the canister through the filter elements to a center passageway where the oil is directed to the center tube.
In both single and double filter element devices, the ends of the filter elements adjacent the collection passages are susceptible to leakage due to the pressures involved. The pressure drop across the filter may be in excess of 90 p.s.i., resulting in substantial compressive forces being exerted hydraulically on the filter tissue. These forces tend to compress and distort the filter element, particularly at the return or exhaust ends thereof.
One solution which has heretofore been used has been to provide an interlocking annular seal which is essentially a ring inserted into the filter element a few layers inwardly of the perimeter of the filter element. A more complete description of such a sealing device as used with an oil filter can be found in U.S. Pat. No. 4,017,400 to Schade. However, it has been discovered that even with such an annular seal, the great hydraulic forces within the filter still result in deformation of the filter element. This causes flow channels to form which allow fluid to flow around the annular seal and thus bypass entirely the filter element. The result is that a significant amount of unfiltered oil is recirculated without removal of much of the contaminants.